因为x1=kx1,x2=kx2
所以将x1=kx1,x2=kx2代入(x2-x1)^2+(y2-y1)^2=(x2-x1)^2+(kx2-kx1)^2=(1+k^2)(x2-x1)^2
故弦长AB=根号下(x2-x1)^2+(y2-y1)^2=根号下(1+k^2)(x2-x1)^2
因为x1=kx1,x2=kx2
所以将x1=kx1,x2=kx2代入(x2-x1)^2+(y2-y1)^2=(x2-x1)^2+(kx2-kx1)^2=(1+k^2)(x2-x1)^2
故弦长AB=根号下(x2-x1)^2+(y2-y1)^2=根号下(1+k^2)(x2-x1)^2